1. Field of the Invention
This invention relates to the regeneration of the activity of oxidation catalysts, particularly those used to oxidize hydrocarbons and carbon monoxide in automobile exhaust gases. The most familiar such catalysts are those in the catalytic converters of automobiles.
The noxious components in the exhaust gases emitted by internal combustion engines are regarded as being one of the primary causes of air pollution and smog. Reduction of the amounts of these pollutants is now required by law in most industrially advanced countries. By catalytic conversion, the exhaust gases and atmospheric oxygen pass through the catalytic converter where the noxious gases are converted to harmless water, carbon dioxide and nitrogen gas.
However, in time the activity of the catalyst is gradually reduced to the level at which the concentrations of pollutants exceed the limits set by the law. At the point, when the catalyst fails to perform as required, it must be replaced with a new one, which is a rather costly event. As the stringency in controlling the emission increases, so does the cost of the catalyst replacement. The most desirable and economical way to eliminate this mounting cost, and also save the expensive noble metals contained in the catalytic converters, such as platinum, palladium and rhodium would be to apply a simple, fast and inexpensive method to restore the activity of the deactivated catalysts. Such a method however, is not known and used up to this time. Now this invention makes this desire a reality.
The actual catalyst regenerations of this invention, performed in converters of cars, prove that this novel process is clean, fast and economical, reduces the hydrocarbon and carbon monoxide pollution by as much as 95%, extends the catalytic activity for a length of time close to that of a new catalyst, and retains, or even improves, the hardness of the catalytic support.
2. Description of the Prior Art
In the prior art, a rejuvenation of automotive emission control catalyst is claimed in U.S. Pat. No. 4,039,471 by exposing the catalyst to reducing atmosphere to reduce the lead and phosphorous contaminants at 300.degree.-700.degree. C. There is no claim on reducing other pollutants, such as hydrocarbons and carbon monoxide which need an oxidizing environment.
U.S. Pat. No. 5,071,802 claims the burning of the carbonaceous materials deposited on the catalyst in the presence of alcohol together with oxygen-containing gas. The difficulty with this process is that the carbon is not the only contaminant, and that the quantity of the carbonaceous matter is unknown. Therefore, the ratio of alcohol-oxygen and carbon are not easily balanced for achieving the required results. An incomplete burning produces more unburned hydrocarbons and carbon monoxide. In addition to these drawbacks, the patent does not apply the process to the exhaust of combustion engines, rather it applies it to the synthesis of organic compounds and cracking petroleum products.
U.S. Pat. No. 3,824,193 uses solution of alkaline metal hydroxides for regeneration of hydrogenation catalyst at 100.degree. to 500.degree. C. Example 10 of this patent shows that its process is ineffective for oxidation catalysts. No claim is made for using this method for regeneration of oxygenation catalysts.
U.S. Pat. No. 4,615,992 describes a regeneration process in which the catalyst is moving down in a pipe reactor against a stream of 3-5% oxygen gas to burn off carbon deposits.
U.S. Pat. No. 4,792,435 discloses generating oxygen gas by decomposing hydrogen peroxide by the platinum group metals deposited on ceramic carriers in heated chambers in a controlled feed rate.
A reference in Chemical Abstract 1986 208666 d refers to a method in which the number 1 plug of a car engine is disconnected and the temperature of the catalyst is allowed to rise to 800-1100 degrees C. for 3-120 minutes. A platinum-cerium-ruthenium catalyst was regenerated at 750.degree. C. in 5 minutes. The emissions of carbon monoxide and nitrogen oxides were reduced from 72 to 94% and from 54 to 60% respectively.
A reference, also in Chemical Abstract 1991, volume 114 ,151432 r, mentions washing a catalyst with water while irradiating with ultrasound. No report on improvement or type of catalyst is given and it was done in a separate vessel and not in an auto converter.
Three references were cited against applicant's parent application Ser. No.972,859, filed Nov. 6, 1992, namely, Jaeger U.S. Pat. No. 1,678,627; Massa et al U.S. Pat. No. 3,460,901; and Erdmannsdoefer U.S. Pat. No. 4,670,233.
Jaeger is directed to a system using an "acidogen" and an oxygen containing gas. The meaning of "acidogen" is not clear but is illustrated as non-metallic acid radical such as nitric acid, sulfur trioxide, sulfur dioxide, etc. The present application does not use such materials nor does it use oxygen as the oxidizing or regenerating material.
Massa et al makes no reference to regenerating an oxidation catalyst but instead teaches the use of solutions of 20-35% hydrogen peroxide in very small amounts of aspirated material to reduce hydrocarbon and carbon monoxide. However there is no teaching that this process continues to decrease these pollutants once the feeding of hydrogen peroxide is terminated. Therefore the treatment does not affect the activity of the oxidation catalyst. Massa et al use more concentrated and more dangerous concentrations of hydrogen peroxide in small aspirated amounts and differs radically from the present process in that there is no regeneration effect. Calculations from the data given in Massa et al show that the amount of peroxide solution per liter of oxidation catalyst is very low and is in an ineffective range.
In the Massa patent, the quantity of the hydrogen peroxide is from 267 times to 12,000 times less then is needed to reactivate a catalyst in a catalytic converter for a motor vehicle.
Table 1 in the Massa patent shows that the highest dosage of H.sub.2 O.sub.2 is 2.5 cubic centimeter 30% H.sub.2 O.sub.2 per minute. EQU 2.5.times.0.3=0.75 gram H.sub.2 O.sub.2
The present application use of H.sub.2 O.sub.2 even at the lowest dosage, is EQU 200 ml.times.1%=200 gr EQU 200 gr/0.75=267 times more
If the preferred quantity, that is, one liter of 10% H.sub.2 O.sub.2 in one minute is used, the dosage is EQU from (200.times.10)/0.75=2,267 EQU to (1,000.times.10)/0.75=6,666 times more
than Massa used in his experiment.
The quantity of the H.sub.2 O.sub.2 Massa used was not even enough to oxidize the CO and hydrocarbon in the test gas. In Table 1, the highest 2.5 cubic centimeter (3rd line in the table) has still left 0.24% of the 0.38% HC (by I.R.), that is 0.091%, which is equivalent to 910 parts per million of hydrocarbon.
This could be because the H.sub.2 O.sub.2 was not enough, or the concentration became too low, or the residence time was not long enough, or a combination of all these. This 910 ppm HC is too much for the present-day clean air regulations. In Florida, for example, the maximum allowable HC emission is 220 PPM. This is expected to be reduced to the 100 ppm level as soon as a method is available for this. The present invention fulfills this requirement.
There are two types of catalyst supports, one support is in bead form, the other is a monolith (honeycomb) form. The volume of the bead support is in most cases about 4 liters. The total surface area of the support is many hundred thousand square inches. Even the much smaller honeycomb support has a superficial surface area of about 15,000 square inches. The actual catalytic surface is many hundred times more. It is obvious, that a 0.75 g quantity of H.sub.2 O.sub.2, even if none of the H.sub.2 O.sub.2 would be consumed by the exhaust gas before it reaches the catalyst, it would not noticably improve the catalyst.
Massa used a single cylinder engine for his experiment, and the volume of the formed exhaust gas was far below that from a present multicylinder combustion engine. Consequently the residence time is from 20 to 200 times shorter in the catalytic converter than in Massa's afterburner. Again, the 2.5 g H.sub.2 O.sub.2 /min. would be too diluted, and the residence time too short to be effective.
Erdmannsdoerfer et al describe a method and means for burning or removing soot collected on the exhaust gas filter of an internal combustion engine, particularly a diesel engine. The soot is ignited and burned off. There is no regeneration of an oxidation catalyst. Again very high concentration, and more dangerous concentration, of hydrogen peroxide (60%), etc., are used.
None of the above teachings anticipate applicant's invention as described herein.